Multi-antenna techniques can significantly increase the data rates and reliability of a wireless communication system. The performance is in particular improved if both the transmitter and the receiver are equipped with multiple antennas, which results in a multiple-input multiple-output (MIMO) communication channel. Such systems and/or related techniques are commonly referred to as MIMO.
The Long Term Evolution (LTE) standard is currently evolving with enhanced MIMO support. A core component in LTE is support of MIMO antenna deployments and MIMO related techniques. Currently one-dimensional (horizontal) antenna array can provide flexible beam adaption in the azimuth domain only through the horizontal precoding process, while fixed down-tilt is applied in the vertical direction.
Recently, it has been found that the full MIMO capability can be exploited through leveraging two-dimensional (2D) antenna planar such that the user-specific elevation beamforming and spatial multiplexing on the vertical domain are possible. Moreover, it was also proposed for the uplink (UL) demodulation reference signal (DMRS) to support additional orthogonal ports for partially overlapping.
Besides, since the channel variation is slow in time domain if a higher center frequency is used, the sparse RS can be used in time domain. In other words, in the future 5G communication, only one or few symbols in time domain for RS transmission is proposed to reduce overhead, wherein a Zadoff-Chu(ZC) sequence was proposed to be used in the new subframe structure. For purpose of illustration, FIG. 1 illustrates one of possible new subframe structures, in which there is only one symbol for RS transmission in one TTI. However, it shall be appreciated that in another possible new subframe structure, the symbol may also be located in another position and/or it comprises more than one UL/DL symbol.
Thus, in the future 5G communication, it is possible to use only one of few symbols of DMRS for both UL and downlink (DL). In such a case, in order to support higher order multi-user MIMO(MU-MIMO), it shall consider using more orthogonal ports for partially overlapping BWs.
Therefore, in the art, a new DMRS design and new reference signal transmission and receiving solutions are required so as to adapt for the new subframe structure with the new channel characteristic variation in the time domain and support more users or more layers.